Image forming apparatuses having a recording head to eject droplets such as ink droplets have been used for printers, facsimiles, copiers, and multifunctional machines, and specific examples thereof include inkjet recording devices. Such image forming apparatuses record images by ejecting droplets such as ink droplets from a recording head toward a recording material such as a paper sheet. Such image forming apparatuses are broadly classified into serial image forming apparatuses in which a recording head ejects droplets while moving in a main scanning direction to form an image on a recording material fed in a sub-scanning direction, and line image forming apparatuses having a fixed line recording head ejecting droplets on a recording material fed in a direction.
In this application, image forming apparatuses mean apparatuses which eject ink droplets so as to be adhered to a recording material such as paper, yarn, fiber, fabric, leather, metal, plastic, glass, wood, and ceramic to form an image thereon. In addition, image formation means not only formation of a meaningful image such as letters and figures but also formation of a meaningless image such as patterns (i.e., mere adhesion of droplets on a recording material). Further, ink means not only so-called inks but also other liquids for use in image formation such as recording liquids, fixing liquids, liquids, and resins. Furthermore, recording material means not only recording sheets such as paper sheets and OHP sheets but also the above-mentioned materials. In addition, image means not only two-dimensional images but also images formed on a three-dimensional object and three dimensional images themselves formed by ink.
There are image forming apparatuses including a maintenance/recovery mechanism (hereinafter referred to as maintenance mechanism) having a cap to cover the nozzle surface of a recording head to prevent drying of the ink in the nozzles and to prevent the nozzles from dusts, and a wiper to wipe the nozzle surface to clean the nozzle surface, so that the nozzles of the recording head can maintain good ink ejecting stability. The wiper performs a recovery operation such that after nozzles discharge an ink (such as ink having an increased viscosity) in a cap, the wiper wipes the nozzle surface so that the ink can form meniscus in the nozzles.
There is a cap for use in such maintenance mechanisms, which includes a peripheral portion contacting the nozzle surface of a recording head on which nozzles to eject ink are formed; a bottom portion forming a closed space above the nozzle surface of the recording head together with the peripheral portion; a suction hole formed on the bottom portion to be connected with a negative pressure generating mechanism to suck the discharged ink; an ink absorbent arranged in the closed space so as to be contacted with the nozzle surface; and a sheet member located between the ink absorbent and the bottom portion and having an opening, at least part of which is connected with the suction hole. The ink discharged from the nozzles toward the cap in a maintenance operation is fed from the suction hole through the ink absorbent and the opening of the sheet member.
In addition, there is a cap for use in such maintenance mechanisms, which caps the surface of vertically arranged nozzles of a recording head and which has an air hole on an upper end portion thereof and a suction hole on a lower side portion thereof.
In the second mentioned cap, the cap is moved horizontally to perform a suction operation. In this regard, in order to prevent dripping of the discharged ink, a capping operation, a head sucking operation, an airing operation of airing the inside of the cap, and a decapping operation are performed in this order as the suction operation.
When such an ink absorbent as mentioned above is arranged in the cap so as to obstruct the air hole, an air bubble problem (non-ink-ejecting problem) is caused in that air fed into the cap in the airing operation and passing the ink-absorbed absorbent forms air bubbles, and the air bubbles enter into nozzles, thereby blocking flow of the ink in the nozzles, resulting in ejection of no ink droplets from the nozzles.
In addition, when the suction hole is occasionally obstructed with the ink absorbent, the suction hole is not connected with the nozzle surface, and the waste ink on the nozzle surface cannot be satisfactorily sucked because the ink absorbent serves as a resistive element, resulting in formation of residual waste ink in the cap. Such residual waste ink is adhered to the nozzle surface in the decapping operation, thereby contaminating the image forming apparatus. In addition, the wiper is easily deteriorated by the residual waste ink, resulting in shortening of life of the wiper.
For these reasons, the inventors recognized that there is a need for an image forming apparatus which hardly causes the above-mentioned air bubble problem while reducing the amount of residual waste ink in a cap even when the recording head of the image forming apparatus is a vertical recording head.